Environmental parameters, including but not limited to, dissolved gases, chemical compounds, solute concentrations, organisms, and ecological communities, are measured to analyze the condition of aquatic and estuarine environments. Measurements are made using a variety of techniques which can be broadly classified as either synoptic (“snap-shots” at a single point in time) or continuous (high frequency measurements over an extended time). Continuous measurement of environmental parameters can be conducted in reference to a fixed location (such as a moored buoy or bridge), in reference to a moving object (such as a vessel), or in reference to a moving parcel of water (such as flowing water in an ocean, river, lake, or estuary).
Portions of the current discussion pertain to environmental parameters being measured in synchrony with the movement of water. Measurement of environmental parameters in synchrony with the movement of water allows measurement of how parameters change along a discrete flow path of water.
In addition to measuring environmental parameters along the flow path of a stream, river, lake, reservoir, or estuary, it is sometimes also the objective of researchers to measure changes in those parameters within a controlled volume of water over time. For example, common experiments include measuring the uptake of nutrients by algae or the degradation of a chemical compound under controlled conditions that simulate some aspect of the natural environment (e.g., sunlight, temperature, fish).
Experiments require a chamber for holding a volume of water and its associated constituents in which measurements of an environmental parameter can be made over time. The chamber isolates the water inside from surrounding water, but may be designed to allow exchange of selected solutes or a size range of particles in the surrounding water. In order to measure these processes along a flow path of water, the chamber should be designed to travel freely with the water surrounding it.